1. Field of the Invention
The present invention relates to a method of emplacing explosives in wellbores, e.g., for explosively fracturing gas- or oil-bearing formations, and to an apparatus for carrying out the method.
2. Description of the Prior Art
Explosives have been used for many years to fracture geologic formations containing oil and gas to improve the rate at which the hydrocarbons flow into the wellbore and thence are withdrawn to a surface collecting system. Explosives used for this purpose, usually high-strength gelatin dynamites containing a high percentage of nitroglycerin, are lowered into the well in rigid cartridges which do not fill the wellbore, leaving an annular space. This operation is hazardous in that subjecting nitroglycerin or nitroglycerin-based dynamite to friction and impact can result in premature detonation particularly in dry, gas-filled holes of the type encountered in the Devonian shale of the Appalachian basin.
Water gel or slurry explosive technology has provided an explosive system in recent years which virtually eliminates friction and impact hazards in loading and handling. There is a need, however, for a means to safely load bags or cartridges of water gel explosive into deep gas-filled wellbores in such a manner that the wellbore is filled from wall to wall to achieve a maximum explosive energy per foot of wellbore. Especially needed is a loading means which achieves a high loading rate, thus minimizing expensive drilling rig time during explosive treatment.